The invention relates to an X-ray examination device having a spot film device, having transport means for the transport of an image layer carrier from a ready position into an exposure position and back, as well as having a speed control for the drive motor.
The spot film devices of X-ray examination devices allow an examination finding determined during fluoroscopy to be retained on a sheet of film. To this end, a sheet of film can be conveyed from a radiation-protected ready position into an exposure position of the spot film device centered relative to the X-ray cone and back. It is thereby of particular importance that the X-ray picture likewise be exposed within the shortest possible time interval after triggering. This is so important because many events in the body of the patient are subject to chronological change as a result of the inherent movement of the organs such as, for example, the lungs, the stomach or the heart, or as a result of the further transport of an injected contrast agent. On the other hand, the transport speed of the sheet of film from the ready position into the exposure position can also not be set too high because the X-ray examination device would otherwise be induced to vibrate given the acceleration and deceleration of the sheet of film or of an image plate and the appertaining film, or respectively, image layer carrier (film carriage, X-ray film cassette, cassette carriage, etc.), said vibrations leading to blurred exposures in the final analysis.
For the purpose of avoiding jolts during introduction of the cassette carriage into the exposure position, it is already known from German Pat. No. 976,870 and from the German AS No. 11 27 704 to allocate electrical and pneumatic anti-vibration elements to the carriage which reduce the acceleration forces, particularly upon entry into the exposure position, and therefore, allow higher accelerations of the image layer carrier or, respectively, of the X-ray film cassette.
In order to be able to shorten the chronological interval between triggering a picture and the exposure thereof even farther, it has been disclosed by the German OS No. 20 51 033 to control the speed of the drive motor for the cassette drive by means of a speed control and, despite high acceleration and deceleration, to thus achieve that the X-ray film cassette enters into the exposure position with a very low, control speed independently of its size and mass. By so doing, only slight deceleration forces occur in the time interval immediately before the exposure. Moreover, exact arresting of the X-ray film cassette in the exposure position is also possible because of the low in-bound speed. Nonetheless, the shortest possible time interval between triggering and exposing the picture attainable therewith is still considered too long. Pictures are exposed too late over and over again.